Impact of Wildfire Emissions: Ozone Precursors and their Contribution to Ambient Pollution

Abstract

In October 2017, the second most destructive wildfire in California history, the Tubbs Fire, sent a plume of smoke across the greater San Francisco Bay area, one of the largest metropolitan regions in the United States. Because wildfires emit many trace gas ozone precursors into the atmosphere, this study aims to quantify the direct effects of the Tubbs fire on ozone pollution in California.

This thesis synthesizes air quality network data along with satellite data to quantify ozone formation downwind of the Tubbs Fire. It also makes use of atmospheric dispersion models to examine plume transport and atmospheric photochemistry. It is important to understand the enhancement of background levels caused by these precursors because they inform the overall production rate of ozone. Local ozone abundance can be reduced by decreasing NOx emissions in a NOx-limited-regime or conversely decreasing VOC emissions in a VOC-limited-regime

The research done in this thesis shows a substantive increase in ozone as a result of wildfire emitted ozone precursors. It shows that in San Francisco, a densely populated urban area, there is a definitive change in the proportion of volatile organic compounds and oxides of nitrogen. Further, it indicates that both Sacramento and San Francisco were at times in exceedance of the National Ambient Air Quality Standards (NAAQS) for ozone while the wildfire plume passed overhead. These wildfires directly impact whether urban areas in California are part of NOx-limited-regimes or VOC-limited-regimes. If wildfires have such an impact in a densely populated urban area, there is a need for further investigation and monitoring on a statewide scale. With a more comprehensive monitoring network, policymakers in Northern California can forecast the impacts a wildfire will have and implement proactive policy to mitigate tropospheric ozone pollution.